Apparatus for applying fluid pressure



nited States Patent 2,728,221 APPARATUS FOR APPLYING FLUID PRESSURE Reuben G. Klammer, China Lake, Calif. Application May 13, 1952, Serial No. 287,579 9 Claims. or. 73-88) (Granted under Title 35, U. s. Code 1952 sec. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to testing machines or other apparatus wherein hydraulic or other fluid pressure is applied to a piston or the like to exert a force upon a test specimen or other object.

The invention will hereinafter be described as a testing machine comprising a ram driven by hydraulic fluid,

although it is obviously not limited to that form of embodiment.

The invention comprehends an apparatus which is capable of maintaining a predetermined load on the specimen being tested, even though the varying deflection in the specimen does not vary directly with'the varying applied force. The invention may also be applied to maintaining a constant force upon the specimen over a period of time, despite progressive deflection of the specimen and fluctuation in the fluid pressure during the period of time.

In a preferred form of the invention, the hydraulic ram is connected to the specimen by a metal member of annular or other shape which is .capable of sustaining the compressive and tensile forces to which it is subjected, yet yielding enough to be materially distorted or deflected thereby. The deflection of said member is utilized to control the supply of fluid to the ram, to thereby maintain the force at the desired value regardless of varying friction in the ram or varying viscosity of the fluid.

It is an object of the present invention to provide an improved and simplified device of the type above indicated.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following description.

Fig. 1 is a diagrammatic view of an apparatus embodying the invention; v

Fig. 2 is a diagrammatic view of a portion of the apparatus shown in Fig. 1, and illustrating one form of valve mechanism;

Fig. 3 is a similar view showing the valve parts in another position; and

Fig. 4 is a similar view illustrating another form of valve mechanism.

The apparatus shown in Fig. 1 comprises a ram including a hydraulic cylinder fixedly mounted in a base 14 in such manner as to sustain either tension or compression. A movable wall which may take the form of a piston 18 is movable in the cylinder by means of hydraulic fluid supplied under pressure from a source 20 and connected to the cylinder by means including a pres sure conduit 22 and a return conduit 23.

The test specimen 26, which may be a wing of an airplane, is shown as extending laterally in cantilever fashion from a fixed support 28, although the invention may be applied to specimens of any type. The rod 30 of piston 18 is joined, by a connection 32 of any suitable type, to the lower of two studs 33, 34 which project diametrically from a ring 36. As above noted, ring 36 should be of suflicient strength to sustain the forces, tensile or compressive, generated by the ram, yet flexible enough to be materially distorted thereby. An apertured specimenengaging member 37 is fitted to the projecting end of specimen 26 by means such as wedges 38 and is secured to the upper stud 34 by a connection 40 which is capable of sustaining either tension or compression.

Within the ring 36 is mounted a servo mechanism comprising a body 42 fixedly secured as by legs 44 to the inner surface of the ring. A valve spool 46 is longitudinally slidable in the body 42, being urged in one direction by a rotary member 50 threaded in a radial bore in ring 36, the position of member 50 at any instant being controlled by a loading control device indicated at 52 and connected by a flexible cable 53 to the member 50. The loading control device is of any suitable known type, and is designed to rotate member 50 as a function of time or other factor. Numeral 51 designates a manual shut-oil valve for cutting off pressure from the source 20.

In the positions of the parts of the fluid valve as shown in Fig. 2, it will be seen that pressure conduit 22 connects with an annular passage 54 formed in spool 46, and that the passage 54 in turn connects with a conduit 56 leading to the upper face of piston 18. v The passage- 54 is of such length that, at ordinary loading, a slight bypass of pressure fluid will take place between the pressure conduit 22 and the exhaust conduit 23; this avoids.

wire-drawing, and results in a less abrupt transition between successive positions of the spool. Leakage past the piston 18 is exhausted through a conduit 60 which communicates with exhaust conduit 23.

With the parts in the positions shown in Figs. 1 and 2, pressure fluid flows to the upper face of piston 18, putting members 30 and 37 under tension, elongating ring 36 in the vertical direction as indicated in broken lines in Fig. 2, and. deflecting the specimen 26 downwardly. Assuming the member 50 to be stationary, it will be seen that a condition of equilibrium will be reached when the specimen has deflected in an amount corresponding to the stress, which is determined by the setting of member 50 by device 52. However, if at that stage the specimen deflects further (as may occur due to such causes as theslippage of rivets in a built-up structural member), the ring 36 will tend to return to its unstressed circular shape. This will permit spring 48 to move spool 46 to the left and body 42 will move to the right in Figs. 1 and 2, which will increase the flow of pressure fluid to the piston and decrease the flow of by-pass fluid to exhaust conduit 23.

' As a result, the piston 18 will move downwardly until the predetermined stress has been reapplied and equilibrium has been restored. Any increase in the leakage past piston 18 or elsewhere in the system will be compensated in a similar manner.

The control device may be caused to move spool 46 to the right until the parts assume the positions shown in Fig. 3. In this situation, passage 54 will be cut off from communication from conduits 22 and 56, while a cross passage 58 will connect conduit 22 to conduit 60 leading to the under face of piston 18, causing it to exert compression rather than tension on the ring 36. At the same time, a second cross passage 62 will connect conduit 56 to conduit 23 to exhaust fluid from the upper face of the piston 18. A restricted duct 64 will at this stage provide a bypass of fluid from the pressure side of the system to the exhaust side, for the purposes above explained. The device will then maintain the pressure determined by the setting of member 50 in a manner similar to that explained above in reference to tension.

3 It will be seen that ring 36 will respond to compressive stress by changing to the form of an ellipse having a horizontal major diameter, and this will permit spring 48 to move spool .46 to the left, permitting morefluid to P ss to the cy nde and a i g h pp ed fo ce at the value determined by the position of member .50. Tensile stress in ring 36 will produce the opposite ,efiect.

In the valve mechanism shown in Fig, 4, the parts are the same, and are designated by the same reference numerals, as in ,Figs. l3. In this form of the invention, however, the conduit 69 is omitted, and the spool 46 is formed with the annular passage 54 as in ,Figs. 143, but has but a single duct 70 which comes into play only when the spool is moved well to the right, whereupon it acts to eli e a l pre ur f om the ppe e o p s on 8 W th his f rm of al e h app s s b o y fo exe in a do n ard force o th spec m n n e t er f rm of t e ention a t ain g ge ind a ed d a r mm i ll a 74 may b mo nted 1 r ng 36 to register the distortion of the ring, and thence the magnitude of the applied load, through any suitable mean su h a e d a a in s ake m t e gauge 74 are the more accurate and reliable because they record directly the deflection of a member directly subjected to the stress'being measured.

Obviously many modifications and variations ofthe present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

ha 'is cl i is:

1. Force applying apparatus comprising fluid pressure means for generating a force in either of two directions, an annular member connected to said means for transmitting said force to an object, and valve mechanism mounted in said member and extending thereacross trans.- versely of the direction of the applied force for regulating the supply of fluid to said means in response to a change in shape of said member, comprising two elements telescopically arranged, one of which is connected to the inner surface of said member, screw means extend" ing through the wall of said member at a point diametrically opposite the point where one of said elements is connected and contacting the other element, and means connected to said screw means for moving same to adjust the position of said other element relative to said one of ai elements- 2. The invention defined in claim 1, comprising in addition means contacting said member for indicating deflection thereof,

3. Force applying apparatus comprising fluid pressure operated means for generating a force, a member connect o said e n or t s i t ng a o ce o an i t and e orm b e y s d ce a ondu t o sunp yin p e sur fluid to sa me ns, val e mec an sm .0 2- trolling the rate of flow through said conduit and in? one of which is operatively connected to said member to e be moved by deformation thereof.

5, The invention definedin-claim 4, wherein the valve mechanism is selectively operative to supply pressure fluid to either face of said wall while exhausting fluid from he opposi f t e ev 6 1 Q e apply ng apparatus s mpt g a pre u fiuid p a more: g ne atin "a f c a es li t member operatively conn ct d o sa d motor r transmitting said force to an object and deformable by said force, a conduit for supplying pressure fluid to said motor, valve mechanism controlling the rate or" flow through said conduit and including two relatively movablevalve:

elements one of which is operatively connected to said member to be actuated 'by deformation thereof, and automatic means for adjusting the position of the other of said elements.

7. The invention defined in claim 6, wherein said memher is of generally toroidal shape and the valve mechanism'is disposed Within the aperture thereof.

8. Apparatus fQI applying force to an object, compris ing means actuated by fluid pressure for generatingaforce, a member connecting said means and said object for transmitting the :force to the object and deformable by said force, and means responsible to the degree of defor-' mationof said member for varying by infinitesimal increments the supply of pressure fluid to said means.

The n i n defined in c a m whe ein sa d emher is of annular form, and said varying means comprises i a servo valve having its relatively moving parts connected to spacedportions of said member. 

